William Hague used this month's British presidency of the UN security council today to focus world attention on the upcoming referendum in southern Sudan in an attempt to prevent the region sliding back into decades-long civil war.

The 9 January referendum will seal the fate of southern Sudan with huge implications for the rest of Africa, and there are dangerous signs that the peace process is unravelling. There have been reports of rising cross-border incursions and tension is running high in hotspots across the area. The foreign secretary told a special meeting of the 15-member security council in New York that this was a "defining moment for Sudan and its people. It is a period of great risk, and therefore a situation that the security council cannot ignore."

The referendum will allow the people of the largely Christian and animist south to decide whether or not to break off from the Arab-dominated north and form their own nation. It would mark the completion of the comprehensive peace agreement between the Sudanese government and the Sudan People's Liberation Army in the south that in 2005 ended almost 40 years of bloody civil war.

Representatives of both sides attended the security council meeting, sitting at opposite ends of the assembly.

The British government has been prioritising Sudan during its presidency of the security council, partly in recognition of the historic role played by Britain in creating the problem in the first place. The decision of the British in 1956 to attach southern Sudan to the ethnically distinct north rather than to allow it to form part of a west African union was an important factor behind the problems that have troubled the area ever since.

As the largest country in Africa and the Arab world, the success or failure of the Sudanese referendum has enormous potential ramifications throughout the region. If the south opts for secession it would become the first new state in Africa since Eritrea split from Ethiopia in 1993.

A great deal is also riding on the referendum in terms of the inner stability of Sudan. Hague reminded the security council that over the past half century more than two million people have died and many more millions been displaced by internal strife.

The US government is also applying its muscle to the region, attempting to entice the Sudanese government to stay on the path towards peace with a bundle of inducements. The secretary of state Hillary Clinton said that the Obama administration had promised to take Sudan off the US list of states that sponsor terrorism if Khartoum co-operated with the referendum.

"We are well aware that it takes not only skill but courage of Sudan's leaders of both north and south to work towards a durable peace," Clinton told the security council.

As a further carrot, the US has stepped up its agricultural aid to the country and is working with the UK and other governments to reduce Sudan's debt burden.

Despite reassurances from Khartoum that the Sudanese government is committed to the success of the referendum, humanitarian groups are braced for a slide back into violence and conflict. They fear that the 30,000 peacekeepers on the ground will prove inadequate should flare-ups occur.

Darfur remains a key hotspot with intensifying aerial bombardment by the Sudanese forces and inter-tribal warfare. One in 10 inhabitants is still living in camps and almost 3 million have been forced from their homes, while the Sudanese president Omar al-Bashir is under arrest warrant from the International Criminal Court for genocide in Darfur.

In the south, the future of the oil-rich area of Abyei also hangs in the balance, with talks over a possible referendum on its status on hold while Bashir attends the hajj in Saudi Arabia.